Merge branch 'codex/simp-agent-entry-state' into codex/simp-unify-agent-session-id

# Conflicts:
#	packages/ui/stdio-agent/README.md

packages/fs/tool-fs/README.md

@@ -47,3 +47,59 @@ The tool passes `exec` (the tool-execution context) as the opaque `actor` on eve
 `fs/observed` fires AFTER the read/write/edit already succeeded, via a plain `ctx.emit`. A listener is contractually a synchronous, side-effect-only recorder (`@deepseek-ai/dsh-fs-policy`'s is a `WeakMap.set`); the tool does not guard the emit, so a listener that throws would surface as the tool's `isError` result — async or fallible observation does not belong on this event.
 
 The read rendering (line windowing + output formatting) lives in `src/read-render.ts` (Cordis-free, independently unit-tested); `src/read.ts`/`write.ts`/`edit.ts` are the tool executors and `src/index.ts` composes them.
+
+## Model Experience
+
+### System prompt
+
+**What the model sees**: Every request in this plugin's registration scope receives the independently registered read, write, and edit guidance below. Scoped tool restrictions can hide schemas without removing these sections.
+
+**Token effect**: Fixed guidance cost per request while the plugin is active, even when a restriction hides one or more tools.
+
+#### Read guidance
+
+```markdown
+Use the read tool — not shell commands like cat — to inspect text files. Results include line numbers. Use offset and limit to continue reading large files.
+```
+
+#### Write guidance
+
+```markdown
+Use the write tool to create files or completely replace file contents. Existing files are overwritten, so read an existing file first (the default fs-policy requires it) and prefer edit for targeted changes.
+```
+
+#### Edit guidance
+
+```markdown
+Use the edit tool for targeted changes to existing UTF-8 text files. It replaces literal old_string with new_string; by default old_string must appear exactly once. If old_string appears multiple times, provide a more specific old_string or set replace_all to true. Read the file first (the default fs-policy requires it), unless you just created or edited it in this session.
+```
+
+### Tool schemas
+
+**What the model sees**: The model sees the generated [`read`, `write`, and `edit` schemas](../../../docs/tool-catalog.md#deepseek-aidsh-tool-fs), with snake_case arguments. Scoped tool restrictions can remove any definition for one agent.
+
+**Token effect**: Fixed schema cost on every request in that tool view.
+
+### Read result
+
+**What the model sees**: A successful read is exactly `<path><displayPath></path>`, newline, `<type>file</type>`, newline, `<content>`, numbered lines as `<lineNumber>: <text>`, a blank line, one footer, and `</content>`. The footer is exactly `(Output capped. Showing lines <start>-<end>. Use offset=<next> to continue.)`, `(Showing lines <start>-<end> of <total>. Use offset=<next> to continue.)`, or `(End of file - total <total> lines)`. A long line ends exactly `... (line truncated to <max> chars)`.
+
+**Token effect**: Read output is capped by `readLimit`, `readMaxLineLength`, and `readMaxBytes`; the retained call and result are resent until compaction.
+
+### Write and edit results
+
+**What the model sees**: Write returns the exact five-line envelope `<path><displayPath></path>`, `<type>file</type>`, `<content>`, `Created file` or `Updated file`, then `</content>`. Edit returns exactly `The file <displayPath> has been updated successfully.` or, for `replace_all`, `The file <displayPath> has been updated. All occurrences were successfully replaced.` The full write or replacement text remains in the assistant tool-call arguments.
+
+**Token effect**: Success text is small, but large mutation arguments and any result are resent until compaction.
+
+### Tool errors
+
+**What the model sees**: Failures are normalized as `Error: <message>`. This package's stable validation and read messages are `file_path must be a non-empty string`, `limit must be less than or equal to <max>`, `old_string must be a non-empty string`, `old_string and new_string must differ`, `cannot read "<path>": not found`, `cannot read "<path>": not a regular file`, and `offset <offset> is out of range for "<path>" (<total> lines)`; provider and policy templates are quoted in their package READMEs.
+
+**Token effect**: Only a failing call adds these retained tokens.
+
+## Known Limitations and Deferred Work
+
+- **No directory-listing, glob, grep, or search tools ship** — a deferral of [the tool-schemas RFC](../../../docs/rfc/implemented/feature/2026-06-17-filesystem-tool-schemas.md); `ctx.fs.listDir` serves provider code such as skill discovery but still has no model-facing consumer, so models fall back to `bash`.
+- **`read` handles UTF-8 text files only** — binary-safe reads and PDF/image/multimodal content are deferred; a directory target is `FS_NOT_REGULAR_FILE`.
+- **No timeout surface** — `read`/`write`/`edit` take no timeout argument and declare no `timeout-policy` budget; cancellation rides `exec.signal` only (the deliberate [fs-family stance](../README.md)).